The M247 HEAT warhead was deemed as compatible with the CRV-7 and thus was added in game. All of the other Warheads that could be fitted are not combat effective (gameplay wise) against the type of armour or conditions the aircraft would face, hence why the current HEAT one was added as its more useful than any of the other options would be in game. There is a suggestion open already for some of the other options to be added, but thus far all the information on them points to the fact they would be worse from a gameplay perspective than the current rocket warheads.
As always, if you have any further information on any of the other warheads that says otherwise, we would be happy to forward that onto the devs for their consideration. However it was fully intentional to add M247 as all data the developers have point to the conclusion its like any other warhead compatible with the Hydra-70 / FFA. The other warheads would be a gimmick at best with the current data on them.
Flame and Gunjob have already covered this, but just to also add in. We explored this further and as far as possible all evidence points to what they have already clarified. It was done for museum purposes only. There is no evidence of any Jaguar model (GR.1A included) carrying more than 2 missiles at a time. The overwing pylons took over the wiring from the underwing stations to free them up for additional ordinance.